1. Field of the Invention
The present invention relates to a seat belt retractor having a comfort mechanism. Particularly, the present invention relates to a seat belt retractor having structure for preventing damage to parts of the comfort mechanism due to the of a wind-up spring.
2. Description of the Prior Art
Seat belt retractors having comfort mechanisms are known. U.S. Pat. No. 3,834,646 discloses a seat belt retractor having a comfort mechanism. The seat belt retractor disclosed in U.S. Pat. No. 3,834,646 includes a spool which is supported for rotation by a retractor frame. Seat belt webbing is connected at one end to the spool and is wound onto the spool for storage. The spool is rotatable in a belt withdrawal direction and in a belt retraction direction. A wind-up spring is connected between the spool and the retractor frame to bias the spool to rotate in the belt retraction direction. The wind-up spring tends to pull the belt webbing against the vehicle occupant.
The comfort mechanism of U.S. Pat. No. 3,834,646 counteracts the force of the wind-up spring and comprises a comfort ratchet wheel, separate from an emergency locking ratchet wheel, connected to the spool for rotation with the spool. A plurality of ratchet teeth extend radially outward from the comfort ratchet wheel. A comfort pawl is supported for pivotal movement by the retractor frame. The comfort pawl is movable from a position spaced from the comfort ratchet wheel to a position engaging one of the teeth on the comfort ratchet wheel. This engagement blocks rotation of the spool in a belt retraction direction. The wind-up spring is, thus, prevented from exerting a force through the spool and belt webbing against the vehicle occupant.
The comfort pawl and comfort ratchet wheel are preferably made to be relatively light in weight. Thus, the comfort pawl and comfort ratchet wheel are often made from plastic or a relatively thin metal and often do not have very high load-carrying capacities. When the seat belt retractor is fully extended, the wind-up spring exerts a maximum force attempting to retract the seat belt webbing. When the seat belt is suddenly released from the fully extended position, the wind-up spring causes the spool and ratchet wheel to rotate at a relatively high rotational velocity. If the comfort pawl engages the comfort ratchet wheel during rotation at this relatively high velocity, there is a chance that the comfort pawl and/or comfort ratchet wheel may damaged or broken.
U.S. Pat. No. 4,227,661 discloses a reeling device for a hose and which includes a structure for preventing damage to a pawl and ratchet wheel during high velocity rotation of a reel and the ratchet wheel by a wind-up spring. The reeling device is constructed similar to a seat belt retractor in that the reel is supported for rotation in retraction and withdrawal directions. A spring biases the reel to rotate in a retraction direction. A ratchet wheel is connected to the reel for rotation with the reel. The ratchet wheel has a plurality of recesses spaced thereabout. A pawl is supported for pivotal movement and may engage one of the recesses to block rotation of the reel in the retraction direction under the bias of the wind-up spring. The ratchet wheel also includes a plurality of cam surfaces each of which are located immediately adjacent and in front of a respective one of the recesses when the ratchet wheel rotates in the retraction direction. Each cam surface is configured to prevent the pawl from falling into one of the recesses during rotation of the spool at a velocity higher than a predetermined velocity.
Placing a cam surface ahead of a recess in a ratchet wheel in a seat belt retractor would not be feasible. This is because the close spacing between the teeth on the comfort ratchet wheel of the seat belt retractor does not permit such cam surfaces to be located between the teeth. If a cam surface was placed ahead of every tooth, the comfort ratchet wheel would have to be made prohibitively large in diameter to accommodate a reasonable number of teeth for a reasonable number of comfort positions.